Conventional optical switches are roughly divided into two groups, i.e., those in which light intensity is modulated by changing the refractive index of the material constituting an optical switch element and those which are allowed to perform the optical switch function by changing the extinction coefficient of the material constituting an optical switch element. As such optical materials employed in these optical switches, inorganic materials have conventionally been known, but organic nonlinear materials, such as m-nitroaniline (mNA), have been coming into use. Because of their large nonlinear optical constants and high response speeds, organic nonlinear materials are coming to be a useful material.
On the other hand, optical switches employing a photocoupler of the type in which optical fibers have been fusion-coupled are also attracting attention with progressing techniques for producing this type of optical switches.
FIG. 3 is a diagrammatic view of that optical switch employing an optical fiber coupler which is described in U.S. Pat. No. 4,786,130. In FIG. 3, numeral 1 denotes optical fibers, 2 a photocoupler part, 3 a coupler housing, 7 a medium whose refractive index changes with temperature, 8 a temperature control unit, and 9 conductors. In this optical switch, the temperature of the medium 7 surrounding the photocoupling part 2 where the optical fibers have been fusion-bonded is controlled by the temperature control unit 8, thereby changing the refractive index of the medium so as to change the branching ratio in the photocoupler. As the material for the medium 7, a silicone oil, a liquid crystal, or the like is used.
Such an optical switch employing an optical fiber coupler is excellent in optical fiber connection and is low-loss. However, the technique of controlling the refractive index of the medium surrounding the fusion-bonded part by changing the temperature of the medium is unpractical because there is a considerable response delay.